This application relates generally to disc drive servo track writers, and more particularly to a servo track writer that is filled with a relatively low-density gas during the servo writing process.
A disc drive typically includes a base to which various components of the disc drive are mounted. A top cover cooperates with the base to form a housing that defines an internal, sealed environment for the disc drive. The components include a spindle motor, which rotates one or more discs at a constant high speed, and an actuator assembly for writing information to and reading information from circular tracks on the discs. The actuator assembly includes a plurality of actuator arms extending towards the discs, with one or more flexures extending from each of the actuator arms. Mounted at the distal end of each of the flexures is a read/write head, which includes an air bearing slider enabling the head to fly in close proximity above the corresponding surface of the associated disc during operation of the disc drive. When the disc drive is powered down, the heads may be moved to a landing zone at an innermost region of the discs where the air bearing sliders are allowed to land on the disc surface as the discs stop rotating. Alternatively, the actuator assembly may move (unload) the heads beyond the outer circumference of the discs so that the heads are supported away from the disc surface by a load/unload ramp when the drive is powered down.
Disc drives typically include a servo system for controlling the position of the heads during both seeking operations (moving from one track to another) and read/write operations where the head must precisely follow the circular track. One type of servo system is a dedicated servo system where one entire disc surface contains servo information written as dedicated tracks. The remaining disc surfaces within the drive are thus used to store data on dedicated data tracks. Another type of servo system, known as an embedded servo system, provides servo information on each of the disc surfaces embedded between data portions. Well known state estimator circuitry is used to estimate the position of the heads at such times that the heads are not located over the embedded servo information.
With both dedicated and embedded servo disc drives, servo information or patterns are typically recorded on the target disc by a servo-track writer assembly (xe2x80x9cSTWxe2x80x9d) during the manufacture of the disc drive. One conventional STW records servo patterns on the discs following assembly of the disc drive. In this embodiment, the STW attaches directly to a disc drive and uses the drive""s own read/write heads to record the requisite servo patterns to the mounted discs. An alternative method for servo pattern recording utilizes a separate STW apparatus having dedicated servo recording heads for recording servo patterns onto one or more discs simultaneously prior to the assembly of such discs within a disc drive.
Regardless of whether the servo information is written to the discs prior to assembly within a disc drive (i.e., using a separate STW apparatus having a dedicated actuator assembly) or following assembly of a disc stack within a disc drive (i.e., using the actuator assembly of the disc drive), it is crucial to provide a highly accurate positioning system with the STW to ensure accurate placement of the servo information on the discs. Specifically, a STW includes a positioning system for moving the actuator assembly and the attached heads across the disc surfaces during the servo writing procedure. The STW further includes a highly precise position detection system (often times incorporating a laser) for determining the position of the actuator assembly during the servo writing procedure. The position detection system provides correction signals to a motor within the positioning system to correct any errors in the position of the servo heads during operation of the STW.
In a continuing effort to store more data onto existing or smaller-sized discs, the disc drive industry is continually attempting to increase the capacity of each disc or platter by increasing the track density (i.e., the number of tracks per millimeter). Increased track density requires more closely spaced, narrow tracks and therefore enhanced accuracy in the recording of servo-patterns onto the target disc surface. However, as the track density increases, it becomes increasingly likely that errors will be encountered during the servo writing process. For example, the servo writing head may experience resonance vibrations during operation, which alters the position of the head as the servo information is written. Such vibrations can lead to inaccurate servo information being written to the disc surface which, in turn, limits the ability of the disc drive to accurately position the data head over the desired data track during normal track following procedures (i.e., during normal read and write operations).
The resonance vibrations experienced by the head during the servo writing process are typically caused by the high-speed rotation of the discs within the STW. That is, regardless of whether the STW utilizes the disc drive itself or a separate, dedicated apparatus, the rotation of the discs within the STW (at speeds of up to 10,000 revolutions per minute or more) causes a great deal of air turbulence within the STW. This turbulence results from friction between the spinning disc surfaces and the air within the STW and represents a known phenomenon in the disc drive art. The air turbulence within a STW also impacts other components within the STW such as the actuator arms and the heads flying over the discs.
One proposed solution for reducing air turbulence while writing servo information to the discs within a previously assembled disc drive is to partially fill the drive with helium gas during the servo writing process, thereby reducing the overall density of the gas within the disc drive. Specifically, reducing the density of the gas within the STW acts to reduce the frictional forces applied to the spinning discs, thereby reducing the drag-induced vibrations on the discs and the actuator assembly. Such solution relates only to STWs where the magnetic discs have already been assembled within the drive. Additionally, a key disadvantage to this solution is that it is difficult to maintain desired helium concentrations within the disc drive due to the tendency of the helium gas to escape the confines of the drive during operation of the STW.
Accordingly there is a need for an improved STW that can maintain desired concentrations of helium or other low-density gases in a cost-effective manner. Furthermore, there is a need for both a helium-filled STW that works with previously assembled disc drives as well as a helium-filled STW that has dedicated servo heads for writing servo information to discs prior to assembly of the discs within a disc drive. The present invention provides a solution to this and other problems, and offers other advantages.
Against this backdrop the present invention has been developed. In accordance with one embodiment of the present invention, a method writes servo patterns on a disc in a servo track writer (xe2x80x9cSTWxe2x80x9d) filled with a low-density gas to reduce drag-induced vibrations during the servo writing process. The method includes loading the disc within the STW and sealing the STW to form an enclosed interior environment. The sealed STW is then filled with a low-density gas until the concentration of the low-density gas within the STW preferably reaches a predetermined level. The STW is then activated to write servo patterns on the disc within the low-density gas environment of the STW. In one embodiment, the low-density gas may be purged from the STW and recycled at the conclusion of the servo writing procedure. The disc may be preinstalled within a disc drive, which in turn is loaded within the STW. Alternatively, the STW may comprise a multi-disc writer (xe2x80x9cMDWxe2x80x9d) having a plurality of dedicated servo writing heads, wherein a stack of discs are loaded within the MDW. The servo writer includes a cover having a sealable opening for loading either the disc drive in the STW or for loading a disc stack within the MDW. When the low-density gas is to be recycled, the purged gas is directed from the STW or MDW to a gas recovery system that separates the low-density gas from air. In one preferred embodiment, the predetermined concentration of the low-density gas is at least 50 percent.
When the STW supports a separate disc drive, the method further includes powering up the disc drive in an air environment prior to filling the STW with the low-density gas, and then powering down the disc drive in an air environment after purging the low-density gas from the STW. On the other hand, when the MDW is optimized for use in a low-density gas environment, the method includes loading the dedicated servo writing heads onto the disc surfaces after the MDW is filled with the low-density gas, and then unloading the heads from the disc surfaces before purging the low-density gas from the MDW.
Another embodiment of the present invention is a servo writing assembly that includes a STW having a base for supporting a spindle motor that rotates the disc and a servo writing head that writes servo patterns on the rotating disc. A cover attached to the base forms an enclosed interior environment within the STW and includes a sealable opening for loading the disc within the STW. The cover further includes an inflow port for directing the low-density gas from the source into the interior environment of the STW prior to writing servo patterns on the disc and an outflow port to allow the low-density gas to be purged once the servo patterns have been written to the disc. In one embodiment, a gas recovery system connected to the outflow port separates the purged low-density gas from air.
When the disc, the spindle motor and the servo writing head are all preinstalled within a disc drive, the drive is inserted through the sealable opening in the cover and fixed within the interior environment of the STW. A conduit then connects the inflow port on the cover to an opening formed in the disc drive to direct the low-density gas to an interior of the disc drive. Alternatively, when the STW includes a plurality of dedicated servo writing heads, the spindle motor supports a plurality of discs for simultaneous servo pattern writing to each disc prior to installation of the discs within a disc drive. The discs are inserted through the sealable opening in the cover and fixed to the spindle motor within the interior environment of the STW.
The present invention can further be implemented as a servo writing assembly having a STW connected to a source of low-density gas for filling the STW with low-density gas prior to writing servo patterns on a disc, as well as means for recovering the low-density gas subsequent to writing the servo patterns on the disc. The gas recovery means preferably includes means for purging the low-density gas from the STW and means for separating the low-density gas from air. In one embodiment, the disc is preinstalled within a disc drive and the means for recovering the low-density gas includes a cover mating with a base of the STW to define a sealed interior environment within the STW. The cover includes a sealable opening to allow insertion of the disc drive within the STW. Alternatively, the STW has a plurality of dedicated servo writing heads for writing servo patterns simultaneously to a plurality of discs in a disc stack and the means for recovering the low-density gas includes a cover mating with a base to define a sealed interior environment within the STW. The cover includes a sealable opening to allow insertion of the disc stack within the STW.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.